On October 9, 2023 I attended the IEEE Engineering Milestone for Perpendicular Magnetic Recording (PMR) in Sendai Japan as the President-Elect for the IEEE (see the image of the milestone plaque below). Work on PMR began at Tohoku University in Professor Emeritus, Dr. Shunichi Iwasaki’s laboratory in 1977. Today all of the hard disk drives used to store most of the world’s data are using PMR.
I met Dr. Iwasaki in 1978 at the University of Minnesota at Dr. Jack Judy’s laboratory and my graduate work at the University was investigating the properties of CoCr perpendicular magnetic anisotropy magnetic media. I have visited the PMR laboratory at Tohoku University several times over the years and have interacted with Dr. Iwasaki and his colleagues many times. It was very satisfying for me to meet many of them at the IEEE milestone event.
Dr. Yoichiro Tanaka, a former student of Dr. Jack Judy and Dr. Iwasaki and also formerly with Toshiba but now a professor at Tohoku University, gave a talk on this history of PMR and its introduction into magnetic recording. I will include some images from his talk to discuss this history. The image below shows the basic concept of PMR as it has been implemented in hard disk drives.
PMR as implemented in HDDs has a magnetic layer with the preferred magnetic recording orientation out of (or perpendicular) to the plane of the media. A special write structure is used to provide magnetic write fields perpendicular to the plane of the media (the single pole recording head) and this perpendicular field is increased by a soft magnetic layer beneath the PMR recording layer, which enhances the perpendicular field from the write head. A magneto-resistive read element (GMR) is used to read the magnetic fields from the recorded information on the media.
Before PMR was implemented into commercial hard disk drives starting in 2005 all commercial hard disk drives used longitudinal magnetic recording, where the magnetic information was written in the plane of the media. With perpendicular magnetic recording the magnetic information is written perpendicular to the plane of the media. These two ways of recording information are shown below. The reason why PMR is attractive is that it allows more stable recorded information at high linear densities and thus enables higher density magnetic recording.
Much of the early work on PMR was done with flexible media (such as floppy disks), although there was some early work on making PMR hard disk drives in the 1990’s. There were many things that had to be done to make commercial PMR storage devices and while PMR was being developed the HDD companies kept making extraordinary advances in the density of longitudinal (in-plane) magnetic recording.
By the late 1990’s and early 2000’s the areal density of HDDs was increasing over 100% each year using longitudinal recording. It was only in the early 2000’s that longitudinal magnetic recording areal density gains became difficult to achieve because of the thermal instability of very small magnetic recording regions using this technology. It was then that the 20+ years of research on PMR began to bear fruit.
In 2005 Toshiba became the first HDD company to introduce PMR-based HDDs. The first product, at 40GB 1.8-inch HDD, for mobile and consumer electronics applications, is shown below. By the beginning of 2007 all the HDD manufacturers were producing PMR HDDs, and by 2010 all shipping HDDs were using PMR.
PMR hard disk drives have enabled significant increases in data storage capacity on HDDs. Today’s HDDs have an areal density (the amount of information that can be stored in a given area of the HDD surface) of over 1 Tera bits/in2 (about a ten-fold increase since the first PMR HDD in 2005).
Future refinements of hard disk drives, such as heat assisted magnetic recording (HAMR), to enable increased magnetic recording density will do so with PMR magnetic media. Using enhancements such as HAMR using PMR the HDD industry projects that it can make HDDs with areal densities of 10-20 Tb/in2, more than a 10-fold increase from today’s HDDs and enabling HDDs with storage capacities over 100TB, in the next decade.
Perpendicular magnetic recording was celebrated as an IEEE Engineering Milestone in Sendai Japan. PMR will be used in future HDDs with other technologies and will result in storage capacities of over 100TB.
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